Re: Shed Insulation advice please

I agree with many of the posters who suggest adequate ventilation. My
railway is in the garage not the shed but I have a couple of older layouts
stored in the shed my wife says I must call the summerhouse (to distinguish
it from the shed that looks like a shed or the one that looks like an
outside toilet) . They don't seem affected by winter conditions (usually
quite mild and dry here in SE Essex)but it is worth noting that without
ventilation the temperature inside was very high during summer. It was
necessary to leave the windows open slightly to keep the temperature down.
Tony
"Wolf Kirchmeir" <ElLoboViejo@xxxxxxxxxxxxx> wrote in message news:46d4b1ec$0$31821$9a6e19ea@xxxxxxxxxxxxxxxxxxxxxxx

Dragon Heart wrote:

Vermin will eat through anything if they can smell something to eat on
the other side ... even metal !

Your main problem will be condensation forming in the roof / roof
insulation so ventilation is vital.

Once you go the insulation route, it can quite complicated. It's not
nearly as simple as the inexperienced think. We Canucks have decades of
experience with insulation. And Rule One is, you can never have too much
insulation. It keeps the heat inside in winter and outside in summer. But
insulation also traps warm air, and warm air contains moisture, which has
a regrettable tendency to condense when it hits a cool surface. That means
there will be condensation in the walls, as well. So Rule Two is, provide
adequate ventilation. If you think these two rules conflict, you're right.
Insulating a building as much art as science.

Re insulation:
The more the better. You will be heating the shed to prevent damp, which
attacks the trains and also provides ideal conditions for mildew. That
means a minimum year-round temperature of at least 10C, 15C would be
better. I don't know the R factors (insulating capacity) in metric terms
(see footnote), but I would advise R15 as a minimum, and R20 would be
better yet. Your wallet will thank you when it comes time to pay the
heating bill. I doubt that even with multiple layers of foil you will have
that R factor in only 25mm of insulation, so put in at least two layers of
the stuff that Dragon Heat recommends. Insulation is cheap compared to the
cost of keeping warm.

Make sure you seal the edges of the insulating material so as to create a
continuous membrane before you apply the interior wall cladding. The
material recommended by Dragon Heart appears to have a vapour barrier
built in. There should be no gaps whatever in this vapour barrier. You do
_not_ want water vapour to get inside the wall. The fact that it includes
layers of foil means that it will minimize heat loss through radiation,
which can be considerable through a wooden wall (wood is transparent to
infrared.)

Re: waterproof membranes and ventilation.
We call them "vapour barriers" over here, because that's what they are.
You _must_ have this on the heated side of the wall. Otherwise, the water
vapour carried by the warm air into the insulated spaces will condense on
the cold side of the wall, and that's very bad news. In your case, it's
worse, because you have a vapour barrier on the outside of the shed
already.

It's OK to have an external vapour barrier, but only if there is a vapour
barrier on the inside of the wall, too. Actually, the membrane on the
outside of the house is more of a wind barrier - it helps prevent the wind
from sucking out the warmed air from inside the walls. Thus, this exterior
membrane should _not_ be airtight, as otherwise warm, moist air can be
trapped inside the walls. If it is airtight, make sure that the wall
cavities have openings into the roof spaces, and that the roof is
ventilated enough to allow slow but steady percolation of air through it.
This will help to keep the inside of the walls dry.

Re: floor treatment.
You lose heat through the floor mostly by radiation, so a layer of
foil-backed paper or plastic should do, but you'll have to install another
layer of sub-flooring over it. You shouldn't put the finish layer directly
onto insulating materials.

Re: roof ventilation.
There should be gaps between the rafters to allow external air to drift up
into the roof. I'm guessing that you have a typical shallow gabled shed
roof. If the rafters are merely 3" or 4" deep, you cannot get much
insulation in there, but put in as much as you can. Leave a space about 1"
between the insulation and the roof skin, this will permit the ventilation
that Dragon Heat rightly emphasises. If you have the vertical clearance
inside the shed, install an inch or two of styrofoam insulation inside,
and cover it with drywall (gypsum board). You'll need to install nailing
strips for the drywall, however.

Er, that's about it.

Footnote: The R factor is the inverse of the thermal conductance. IE, the
smaller the heat transfer rate, the higher the R factor. In Canada we use
RSI as the metric equivalent. I don't know if the EU does so. Divide the R
factor by 7 to get the RSI factor.

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